Burgess Shale

Canadaspis perfecta (a crustacean)

Canadaspis is well represented in the Burgess Shale fossil collection by over 4,000 specimens. As a result, its features are well understood and it's been confidently classed as an early ancestor of the crustaceans (currently, the crabs and lobsters.) Here, the artist shows us a lobster-like creature with a segmented "tail", a body partially covered by a chitinous shell (or carapace), and a number of walking legs with their associated gill flaps tucked under. These are critical identification features, although not conclusive. What cinches its ancestral relationship to the present day Crustacea are details in the head appendages which cannot be shown here.

Scientists conjecture that the gill flaps (normally used for "breathing," i.e., oxygen exchange) could also be used for swimming. Some specimens were preserved as if in a frozen "snap-shot" with each limb slightly displaced from the next, as if demonstrating a swimming stroke.